1. Field of the Invention
The present invention relates to an image capturing unit, a color measuring device, an image forming apparatus, a color measuring system, and a color measurement method.
2. Description of the Related Art
In an image forming apparatus such as a printer, processing called “color management” is performed to suppress the variability of outputs due to device-specific characteristics and enhance the reproducibility of the outputs with respect to inputs. The color management is performed in the following steps, for example. First, an image of a reference color chart (or patch) is actually output by an image forming apparatus (in the following, a patch output by an image forming apparatus as an image is referred to as “patch image”), and a color measuring device performs color measurement on this patch image. A color conversion parameter is generated based on a difference between a color measurement value of the color-measured patch image and a color specification value in a standard color space of the corresponding reference color, and this color conversion parameter is set in the image forming apparatus. After that, when outputting an image corresponding to input image data, the image forming apparatus performs color conversion on the input image data based on the set color conversion parameter and outputs an image based on the image data after the color conversion. By this means, the image forming apparatus can perform image output of high reproducibility in which the variability of outputs due to device-specific characteristics is suppressed.
In the above color management, as a measuring device to measure a patch image, a spectrum measurer is widely used. The spectrum measurer can acquire the spectral reflectivity for each wavelength and therefore perform color measurement with high accuracy. However, the spectrum measurer is an expensive device and therefore it is demanded that color measurement with high accuracy can be performed using a cheaper device.
Examples of a method of realizing color measurement at a low cost include that a color measurement target is imaged as a subject by an imaging apparatus having an image sensor and the RGB values of the subject acquired by capturing an image are converted into color specification values in the standard color space. For example, Japanese Patent No. 3129502 discloses a technique of: providing a reference color chart as a comparison target of a subject in a position near the subject of a color measurement target; imaging the subject and the reference color chart by a color video camera at the same time; correcting RGB data of the subject using the RGB data of the reference color chart acquired by capturing an image; and converting the RGB data of the subject into color specification values in the standard color space.
However, in the technique disclosed in Japanese Patent No. 3129502, it is difficult to hold positional relations among a subject, a reference color chart and a color video camera; image-capturing conditions vary every time when an image is captured; and therefore there is a problem that stable imaging may not be performed.
Therefore, there is a need for an image capturing unit, color measuring device, image forming apparatus, color measuring system, and color measurement method capable of performing stable imaging.